Supplementary Material

Fig. S1. Pictures of the upper and lower beaks from the cephalopod species identified in the stomach contents of Scyliorhinus canicula and Squalus blainville sampled in the Aegean Sea.

Table S1. Equations used for the ML reconstruction of the cephalopod species identified in the stomach contents of Scyliorhinus

canicula and Squalus blainville sampled in the Aegean Sea. The maximum ML recorded for each of the species is also presented.

Cephalopod species Common names Equation Reference MLmax Reference Abralia veranyi (Rüppell, 1844) Verany's enope squid ML= -2.103+24.257LRL Öztürk et al., 2007 47* Salman & Laptikovsky, 2005 Pyroteuthis margaritifera (Rüppell, 1844) Jewel enope squid ML= 5.26+26.73LRL Lu & Ickeringill, 2002 40* Mangold & Boletzky, 1987 Histioteuthis bonnellii (Férussac, 1834) Umbrella squid ML= 1.82+15.24LRL Lu & Ickeringill, 2002 330* Mangold & Boletzky, 1987 Loligo forbesii (Steenstrup, 1856) Veined squid ML= -42.22+84.274LRL Clarke, 1986 560* Jereb et al., 2015 Illex coindetii (Vérany, 1839) Broadtail squid ML= 58.18LRL0.816 Lefkaditou, unpubl. 280* Jereb et al., 2015 Todarodes sagittatus (Lamarck, 1798) European flying squid ML= 76.72+27.379LRL Lefkaditou, unpubl. 600* Cuccu et al., 2005 Todaropsis eblanae (Ball, 1841) Lesser flying squid ML= 32.77LRL1.09 Lefkaditou, unpubl. 204* Jereb et al., 2015 ML= 2.31+32.75LRL Onychoteuthis banksii (Leach, 1817) Boreal clubhook squid Lu & Ickeringill, 2002 301* Quetglas et al., 2013 ML = -7.29+37.78URL ML= 21.6LRL0.799 Heteroteuthis dispar (Rüppell, 1844) Odd bobtail Lefkaditou, unpubl. 25 Jereb & Roper, 2005 LRL= 0.878URL1.087 Neorossia caroli (Joubin, 1902) Carol bobtail ML= -1.544+23.411LRL Açik & Salman, 2010 83 Jereb & Roper, 2005 Rossia macrosoma (Delle Chiaje, 1830) Stout bobtail ML= 5.032+18.344 LRL Açik & Salman, 2010 85* Mangold & Boletzky, 1987 Sepietta oweniana (d'Orbigny, 1839–1841) Common bobtail ML= 9.558+14.742LRL Açik & Salman, 2010 40* Jereb & Roper, 2005 Argonauta argo (Linnaeus, 1758) Greater argonaut ML= -1.1670+6.2816LCL Smale et al., 1993 97 Jereb et al., 2015 Octopus salutii (Vérany, 1836) Spider octopus ML= -11.525+38.039LHL Lefkaditou, unpubl. 165* Quetglas et al., 2005 Scaeurgus unicirrhus (Delle Chiaje, 1841) Unihorn octopus ML= 24.962LHL1.049 Lefkaditou, unpubl. 90 Jereb et al., 2015

Abbreviations: N, number of individuals; ML, mantle length; MLmax, maximum mantle length; LRL, lower rostral length; URL, upper rostral length; LHL, lower hood length in mm; *Mediterranean Sea; Common names according to FAO (Mangold & Boletzky, 1987).

Table S2. Summary of the cephalopods prey contribution in the diet of Scyliorhinus canicula in

various locations of the Mediterranean Sea and Atlantic Ocean.

TL range Contribution to diet Area N Cephalopod species Reference (mm) %N %W %O IRI %IRI Abralia veranyi* 6 Pyroteuthis margaritifera* 1 Histioteuthis bonnellii* 1 Loligo forbesii* 1 Illex coindetii 10 Todarodes sagittatus* 1 Todaropsis eblanae 2 Onychoteuthis banksii* 2 AEG 314 209–517 Present study Heteroteuthis dispar 10 Neorossia caroli* 1 Rossia macrosoma* 5 Sepietta oweniana 2 Argonauta argo* 1 Octopus salutii* 1 Scaeurgus unicirrhus 1 Total Cephalopoda 45 0.38 AEG 314 209–517 Total Cephalopoda 30.8 Kousteni et al., 2016a Karachle & Stergiou, nAEG 34 241–451 Total Cephalopoda 50.2 2010 Illex coindetii + Todaropsis eblanae + neAEG 29 139–530 Sepia officinalis + Kabasakal, 2002b Sepia elegans + Sepia sp. + Abralia veranyi 1 ION 1 460 Lefkaditou et al., 2016 Heteroteuthis dispar 4 Heteroteuthis dispar 66.7 13.8 ADR 31 94–485 Bello, 1997 Illex coindeti 33.3 6.90 Sepiola rondeletii 1.80 1.00 3.50 9.80 0.20 Sepia elegans 1.50 1.00 3.00 7.50 0.10 Illex coindeti 1.00 0.90 2.30 4.30 <0.1 ADR 852 104–460 Todaropsis sp. 1.00 0.80 2.30 4.10 <0.1 Šantić et al., 2012 Sepietta oweniana 0.90 0.70 2.10 3.30 <0.1 Unidentified 2.40 1.80 3.50 14.70 0.30 Total Cephalopoda 8.60 6.20 10.3 152.4 3.00 Total Cephalopoda MAL 396 140-520 (Eledone sp., Sepiolidae, 16.4 Gravino et al., 2010 Octopus defilippi) BAL 66 140–46 Total Cephalopoda 0.60 Valls et al., 2011 POR 858 215–610 Loligo vulgaris 0.11 0.33 0.23 Martinho et al., 2012

Sepia officinalis 0.06 0.11 0.12 Octopodidae 0.11 0.70 0.23 Total Cephalopoda 2.40 1.40 3.50 Octopus defilippi 0.70 CAN 13 140–700 Other Cephalopoda 5.80 Olaso et al., 1998 Total Cephalopoda 6.50 CAN 445 120–680 Total Mollusca 3.18 Serrano et al., 2003 CAN 4.362 140–700 Total Cephalopoda 11.0 6.10 Olaso et al., 2005 Octopus vulgaris 0.54 1.22 0.71 1.25 Illex coindeti 0.54 0.47 0.71 0.72 Sepia officinalis 0.82 1.78 1.07 2.78 CAN 975 282–531 Mnasri et al., 2012 Sepiola rondeletii 1.09 0.36 0.71 1.03 Unidentified 1.91 1.40 2.49 8.24 Total Cephalopoda 4.90 5.23 5.69 14.0

Abbreviations: N, number of non-empty stomachs examined; TL, total length; %N, numerical index; %W, gravimetric index; %O, occurrence index by Hyslop (1980); IRI, index of relative importance by Pinkas et al. (1971); %IRI, ranked IRI by Rosecchi & Nouaze (1987); MEDITERRANEAN: AEG, Aegean Sea; neAEG, northeastern Aegean Sea; ION, Ionian Sea; ADR, Adriatic Sea; MAL, off Malta; BAL, off Balearics; ATLANTIC: POR, off Portugal; CAN, Cantabrian Sea; the number of individuals per species is given in italics; +, present; *first record in S. canicula diet

Table S3. Summary of the cephalopods prey contribution in the diet of Squalus blainville in

various locations of the Mediterranean Sea and Atlantic Ocean.

TL range Contribution to diet Area N Cephalopod species Reference (mm) %N %W %O IRI %IRI Abralia veranyi 4 Pyroteuthis margaritifera* 1 Illex coindetii* 3 Todarodes sagittatus* 1 Todaropsis eblanae* 2 AEG 147 182–759 Onychoteuthis banksii* 1 Present study Heteroteuthis dispar 4 Rossia macrosoma* 1 Octopus salutii* 1 Scaeurgus unichirrus 4 Total Cephalopoda 22 37.4 AEG 147 182–759 Total Cephalopoda 51.2 Kousteni et al., 2017 57♂ 160–270 12.2 28.2 16.2 6.99 neAEG Total Cephalopoda Özütemiz et al., 2009 78♀ 170–280 7.35 21.0 10.9 3.28 Sepia elegans 1.98 16.4 24.2 446 neAEG 33 350–420 Unidentified 0.66 6.57 6.06 43.8 Kabasakal, 2002a Total Cephalopoda 2.64 7.54 30.3 309 Abralia veranyi 1 Abraliopsis morisii 3 ION 75 357–780 Lefkaditou et al., 2016 Heteroteuthis dispar 5 Scaeurgus unicirrhus 2 Loligo vulgaris 0.26 1.33 0.43 Sepia officinalis 0.77 1.13 0.86 POR 233 326–796 Martinho et al., 2012 Octopodidae 0.77 4.03 1.29 Total Cephalopoda 3.84 5.20 5.58

Abbreviations: N, number of non-empty stomachs examined; TL, total length; %N, numerical index; %W, gravimetric index; %O, occurrence index by Hyslop (1980); IRI, index of relative importance by Pinkas et al. (1971); %IRI, ranked IRI by Rosecchi & Nouaze (1987); MEDITERRANEAN: AEG, Aegean Sea; neAEG, northeastern Aegean Sea; ION, Ionian Sea; ATLANTIC: POR, off Portugal; the number of individuals per species is given in italics; *fist record in S. blainville diet

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